1. Field of the Invention
The present invention relates to lens driving devices that are generally used for relatively small sized cameras, such as, cameras for portable equipment with camera unit including portable telephones with camera unit. The present invention also relates portable equipment with camera.
2. Related Background Art
When taking pictures with a portable telephone with digital camera unit, the user typically holds the portable telephone with one hand to take pictures of the user's face or other closely located subjects in many occasions. For this reason, many of the photographing lens systems that are used for this type of camera have a close-up photographing function. The photographing lens system with such a close-up photographing function has different lens positions for ordinary photographing and close-up photographing, or macro photographing. Typically, the lens is positioned slightly closer to subject by a predetermined distance than its position in the ordinary photographing.
For this reason, the photographing lens system of the type described above is equipped with a driving source to move the lens to two different positions for ordinary photographing and macro photographing. The driving source is driven with a switch to move the lens between the two different photographing positions. However, for portable equipment such as portable telephones, it is difficult to use a motor as a driving source as it hinders the reduction in size and weight of the equipment. Instead, such portable equipment often uses a lens driving device in which an electromagnetic force is directly used for driving a lens to move the lens.
A lens driving device of the type in which an electromagnetic force is directly used to move a lens is typically equipped with a cylindrical case that retains a lens, a ring-shaped drive magnet mounted on an outer circumference of the case, and a drive coil that opposes the drive magnet. While energization of the drive coil is controlled to magnetically drive the case that retains the lens in an optical axis direction to a designated position, the case is retained at the designated position by a magnetic force.
Also, another lens driving device may be quipped with a case having a lens mounted thereon, wherein the case is rotated in its circumferential direction, and the rotational movement is converted into movements in an optical axis direction such that the case is moved in the optical axis direction.
Still another lens driving device proposed is an electromagnetic actuator for camera that is equipped with a moving body with a coil wound around is freely pivotally mounted on a shaft. The moving body is sandwiched by magnets and yokes from both sides of the moving body in an axial direction. The moving body is swung about the shaft by an electromagnetic thrust that is generated between the coil and the magnets and in a direction parallel with opposing surfaces of the moving body, and swinging motions of the moving body are converted to linear movements of the lens system by a cam mechanism.
However, in the lens driving devices of the type in which the case that retains the lens is magnetically driven in an optical axis direction to a designated position, and the case is magnetically retained at the position, if the lens is to be retained at the position for a long time, the drive coil needs to be energized during that period. For this reason, the lens driving device of this type has problems, namely, it has a large power consumption, and therefore is not suitable for mounting on portable telephones that basically have a limited power supply battery capacity.
In contrast, in the lens driving device of the type in which the case is rotated in its circumferential direction to move the case in a rotational axis direction, i.e., optical axis direction, there is an advantage that the lens driving device has a relatively low power consumption because it does not require an electromagnetic force to retain the case at a specified position. However, the lens driving device of the this type has a complex structure because it needs to convert the rotational force into linear movements, and includes a large number of components, and therefore is not suitable for mounting on portable equipment such as portable telephones.
The electromagnetic actuator for camera described above needs to be equipped with a mechanism that swings the moving body by an electromagnetic force, and a cam mechanism that converts swinging motions into linear movements. As a result, the lens driving device of the this type has a complex structure, and includes a large number of components, and its mechanism spreads outside the lens system. For this reason, its miniaturization is difficult, and therefore it is not suitable for mounting on portable equipment such as portable telephones.